Treating nickel base alloys

ABSTRACT

A method of treating a nickel base alloy so as to produce an alloy having a structure characterized by dispersed discrete fine spherical carbides. The method comprises the steps of casting an ingot of nickel base alloy, homogenizing the ingot at a temperature of from 2,200* to 2,400* F so as to dissolve primary carbides present in the alloy and increase the chemical homogeneity thereof, cooling the alloy at a rate which substantially precludes the precipitation of coarse and film-like carbides at temperatures above 1,900* F and at a second rate in which dispersed fine spherical carbides precipitate at temperatures below 1,900* F; and hot working the alloy at a temperature lower than that at which the primary carbides dissolve.

United States Patent 1191 1111 3, 7 Bailey 1451 Jan. 15, 1974 TREATINGNICKEL BASE ALLOYS Primary ExaminerRichard 0. Dean [75 Inventor: RonaldE. Bailey, New York Mills, Gioia N.Y. i

[73] Assignee: Special Metals Corporation, New ABSTRACT Hartford Amethod of treating a nickel base alloy so as to pro- [22] Fil d; S t 25,1972 duce an alloy having a structure characterized by disperseddiscrete time spherical carbides. The method [211 App! 291859 comprisesthe steps of casting an ingot of nickel base alloy, homogenizing theingot at a temperature of 2] us. c1 148/2, 148/1 1.5 F from 2 to 2,400 Pso as todissolvo P y 1 [51 Int. Cl. C22f 1/10 bidos Present in the alloyand increase the Chemical [58] Field of Search 148/2, 11.5 R, 11.5 Fhomogeneity thereof, cooling the alloy at a rate which substantiallyprecludes the precipitation of coarse and [56] Ref Cit d film-likecarbides at temperatures above l,900 F and UNITED STATES PATENTS at asecond rate in which dispersed fine spherical car- 3,329,535 7/1967Langer et al. 148/1 1.5 F bldes precipitate at temperatures below 1900'F; and

hot working the alloy at a temperature lower than that at which theprimary carbides dissolve.

l7 Claims, 4 Drawing Figures FIG. l

PATENTEU JAN 1 5 m4 FIG.4

FIG. 3

TREATING NHCKEIL BASE ALLOYS The outstanding high temperature propertiesof nickel base superalloys have made their use in turbines and otherhigh temperature applications quite extensive. However, as in all areasof technology, metallurgists and other scientists and engineers areconstantly striving to develop improved alloys. This work has primarilycentered around new alloys with dissimilar chemistries, but has alsoembraced new heat treatments for those already developed, and it is thislatter type of work which led to the present invention.

It has commonly been observed that fracture in nickel base superalloys(particularly in the direction normal to metal flow) occurs by crackpropagation along carbide stringers, and this is especially true whenthe stringers are associated with remnant dendritic segrcgation. Thestringers which include large elongated carbide particles and aligneddiscrete carbide particles or a combination of both, provide paths whichfacilitate fracture.

The present invention provides a sophisticated heat treatment whichdecreases dendritic segregation and minimizes the formation of carbidestringers. Instead of coarse and/or film-like carbides, it produces astructure characterized by dispersed discrete fine spherical carbidesand an alloy with a high degree of chemical homogeneity. As a result thealloy has improved tensile strength and/or tensile ductility and/orstress rupture properties, and particularly in the direction transverseto metal solidification and/or metal flow. More specifically, theinvention involves a high homogenization temperature and criticallycontrolled cooling rates, as well as casting and hot working. Moreover,it is in part based upon processing which was previously considereddetrimental. Previous technical reports have indicated that so calledhigh homogenization temperatures cause a subsequent formation of carbidefilms and thereby decrease ductility.

It is accordingly an object of this invention to provide a method oftreating nickel base superalloys, so as to improve their properties.

The foregoing and other objects of the invention will be best understoodfrom the following description, reference being had to the accompanyingphotomicrographs wherein:

FIG. 1 is a photomicrograph at 50X of an ingot processed in accordancewith the present invention.

FIG. 2 is a photomicrograph at 50X of a billet processed in accordancewith the present invention;

FIG. 3 is a photomicrograph at 50X of an ingot processed in accordancewith prior art techniques; and

FIG. 4 is a photomicrograph at 50X of a billet processed in accordancewith prior art techniques.

Nickel base alloys, having a structure characterized by disperseddiscrete fine spherical carbides, are produced, in accordance with thepresent invention, by a method which comprises the steps of: casting aningot of nickel base alloy; homogenizing the ingot at a temperature offrom 2,200" to 2,400 F, and preferably at a temperature of from 2,250 to2,400 F, thereby dissolving primary carbides present in the alloy andincreasing the chemical homogeneity thereof; cooling the alloy at a ratewhich substantially precludes the precipitation of coarse and film-likecarbides at temperatures above l,900 F and at a rate in which dispersedfine spherical carbides precipitate at temperatures below 1,900 F; andhot working the alloy at a temperature lower than that at which theprimary carbides dissolve. The primary carbides which form during thesolidification of the ingot and/or during the cooling thereof aregenerally MC or M C carbides. MC carbides are comprised of titanium withoptional amounts of molybdenum, nickel, chromium and zirconium, and M Ccarbides are comprised of molybdenum with optional amounts of tungsten,chromium, iron and cobalt. It is essential to dissolve the primarycarbides in order for the desired dispersed discrete fine sphericalcarbides to form during cooling, and in order to do so homogenizationmust be at a temperature of at least 2,200 F. A maximum homogenizationtemperature of 2,400 F is, however, imposed as carbides melt at highertemperatures. Prior to the present invention, it was generally acceptedthat carbide films would subsequently form following homogenization attemperatures as high as 2,2()0 F, and that these films woulddetrimentally affect the alloys ductility. For homogenization, asufficient period of time is preferably allowed for the primary carbidesto dissolve and to permit carbon and other elements to diffuse over adistance at least approaching one half the local dendrite-arm spacing.As a general rule the required period for homogenization is in excess of4 hours, although no specific time period can be set as it is dependentupon the homogenization temperature and the thickness of the ingot. Toobtain the desired carbide structure cooling from the homogenizationtemperature to l,900 F must be conducted at a rate fast enough topreclude the precipitation of coarse and film-like carbides. The coolingrate to 1,900 F must be in excess of 25 F per hour, and is preferably inexcess of F per hour. The cooling rate at temperatures below 1,900 F andduring the period at which precipitation occurs is, on the other hand,one which is intentionally kept down. More specifically, it ismaintained below 125 F per hour and preferably below 60 F per hour. Ofcourse, the cooling rate to 1,900 F is in excess of that employed duringthe period of precipitation at temperatures below l,900 F. No specificnumerical range can, however, be placed upon the period of time at whichprecipitation occurs, as the period is dependent upon both the coolingrate and the thickness of the ingot. Moreover, the cooling rate duringthe period at which precipitation occurs often encompasses holdingperiods, as the desired carbide structure can be obtained by holding thealloy at a particular temperature for a period of time. For example, ifthe alloy is held at l,200 F for 1 hour the 1 hour is included incalculating its cooling rate from l,900 to 1,200 F. With regard to this,a preferred holding temperature is from 950 to l,350 F. After coolingthe alloy is hot worked; e.g., forged, swaged, extruded, rolled, drawnor pressed, within a temperature range of from 1,750 to 2,l F andpreferably within a temperature range of from 1,800" to 2,150 F. Atlower temperatures alloys tend to excessively crack and at highertemperatures they cannot uniformly deform without cracking. The hotworking temperatures and all other temperatures referred to herein, aswell as rates involving temperatures, are based upon furnacetemperatures rather than metal temperatures, as it is more practical totalk about furnace temperatures when discussing production size ingotsand billets. Furnace temperatures are lower than metal temperaturesduring cooling, and cooling as discussed above is a critical part of thepresent invention. Metal temperatures do, however, reach furnacetemperatures during homogenization due to the prolonged exposure attemperature.

The nickel base alloy being treated is most often a gamma primestrengthened alloy and generally, but not necessarily, consistsessentially of, in weight percent: up to 0.2 percent carbon, up to 2.0percent manganese, up to 2 percent silicon, from 5 to 25 percentchromium, up to 20 percent cobalt, up to percent molybdenum, up to 10.0percent titanium, up to 5 percent aluminum, up to 0.05 percent boron, upto 0.5 percent zirconium, up to 40.0 percent iron, up to 8.0 percent ofmetal from the group consisting of columbium, tantalum and hafnium, upto 2.0 percent vanadium, up to 10 percent tungsten, up to 0.5 percentrhenium, up to 0.02 percent of metal from Group 11 A of the periodictable, up to 0.5 percent of rare earth metal, balance essentiallynickel, said percentage of nickel being at least 40 percent. Within thisbroad range an alloy which has proven to be particularly well suited forthe treatment of the present invention consists essentially of, inweight percent, up to 0.15 percent carbon, up to 1.0 percent manganese,up to 1.0 percent silicon, from 15-23 percent chromium, from 10 to 18percent cobalt, from 3 to 6 percent molybdenum, from 2 to 3.5 percenttitanium,

from 1.0 to 2.0 percent aluminum, from 0.0025 to 0.0125 percent boron,from 0.02 to 0.2 percent zirconium, up to 2 percent iron, up to 4.0percent of metal from the group consisting of columbium, tantalum andhafnium, up to 0.5 percent vanadium, up to 0.02 percent of metal fromGroup 11 A of the periodic table, up to 0.5 percent of rare earth metal,balance essentially nickel. Another alloy within the broad range, forwhich there is reason to believe that it is particularly well suited forthe treatment of the present invention, consists essentially of, inweight percent, up to 0.15 percent carbon, up to 2.0 percent manganese,up to 1.0 percent silicon, from 5.0 to 15.0 percent chromium, up to 10.0percent cobalt, from 2 to 7 percent molybdenum, from 1.0 to 3.75 percenttitanium, up to 2 percent aluminum, up to 0.05 percent boron, from 25 to40 percent iron, balance essentially nickel. For purposes of definitiongamma prime is defined, and believed to have, the general composition M(Al and/or Ti and possibly one or more additional metals from the groupcomprised of tantalum, columbium, molybdenum and- /or chromium). As usedherein, the M" portion of the gamma prime is regarded as consistingmainly of nickel of 875 F per hour. Cooling was performed at a ratesufficiently fast to substantially preclude the precipitation of coarseand film-like carbides. From 1,900 F the ingot was cooled at a slowerrate of 33.3 F per hour, to 900 F. Dispersed discrete fine sphericalcarbides precipitated during the cooling from 1,900 F. This desirablecarbide morphology and distribution is seen in FIG. 1 which is aphotomicrograph of the cooled ingot at X. The composition of the ingotwas, in weight percent, 0.06 percent carbon, less than 0.10 percentmanganese, less than 0.10 percent silicon, 19.1 percent chromium, 13.4percent cobalt, 4.15 percent molybdenum, 3.15 percent titanium, 1.34percent aluminum, 0.005 percent boron, 0.06 percent zirconium, 0.9percent iron, balance essentially nickel.

The ingot was subsequently hot worked from 2,125 F and then ground. Morespecifically, the ingot was worked from a 20 inch ingot to a 14% inchoctagon billet and then ground to a l3'A-inch octagon billet. FIG. 2 isa photomicrograph of the hot worked and ground billet at 50X. Note thatthe billet is still characterized by dispersed discrete fine sphericalcarbides.

A number of ingots having a composition, in weight percent, of from 0.05to 0.07 percent carbon, less than 0.10 percent manganese, less than 0.10percent silicon, 18.7 to 19.7 percent chromium, 13.0 to 14.5 percentcobalt, 3.75 to 4.5 percent molybdenum, 2.9 to 3.2 percent titanium,1.30 1.38 percent aluminum, 0.0040 to 0.0055 percent boron, 0.055 to0.075 percent zirconium, less than 1.50 percent iron, balanceessentially nickel, were processed in accordance with prior arttechniques. The ingots were homogenized at a maximum temperature of2,l75 F, subjected to haphazard furnace cooling to a temperature of from1,500 to 1,700 F, air cooled to room temperature therefrom and hotworked from 2,125 F into l4Vs-inch octagon billets which weresubsequently ground to l3%-inch octagon billets. FIGS. 3 and 4respectively show photomicrographs at 50X of one of these typical priorart ingots and billets. Note that the carbides in FIG. 3 are large andangular, and that the carbides in FIG. 4 are concentrated in bands.

Pancake property data for both the alloy treated in accordance with thepresent invention and for the average of the prior art billets is setforth below in Table l. The data which is more indicative of transverseproperties than longitudinal properties clearly shows the value of theheat treatment of the present invention.

TABLE 1 ROOM TEM PERATURE TENSlLE PROPERTIES 1000F TENSILE PROPERTIESSTRESS RUPTURE PROPERTIES 1350Fl80ksi NOTCH v.5. Elongation R i n U.T.S.v.5. Elongation ii duciion Life Elongation (kw (ksi) 1%) f lksil (ksi)1%) or (hrs) Area Area 1%! 1%) Present 201.0 148.0 24.3 29.7 183.0 138.021.2 25.9 47.3 28.4 invention Prior art 190.4 137.5 18.3 22.0 170.8125.0 16.4 19.9 43.0 25.0

with one or more metals from the group comprised of chromium, cobalt,molybdenum and iron.

The following examples are illustrative of the invention.

A nickel base alloy ingot was cast and homogenized for 48 hours at 2,250F. From the homogenization temperature the ingot was cooled to 1,900 Fat a rate 1 claim:

1. A method of treating a nickel base alloy so as to produce an alloyhaving a structure characterized by dispersed discrete fine sphericalcarbides, which comprises the steps of: casting an ingot of nickel basealloy; homogenizing said ingot at a temperature of from 2,200 to 2,400P, thereby dissolving primary carbides present in said alloy andincreasing the chemical homogeneity thereof; cooling said alloy at arate which substantially precludes the precipitation of coarse andfilm-like carbides at temperatures above 1,900 F and at a rate at whichdiscrete fine spherical carbides precipitate at temperatures below 1,900F, said cooling from said homogenizing temperature to 1,900 F being at afirst cooling rate, said cooling at temperatures below l,900 F andduring the period at which precipi' tation occurs being at a secondcooling rate, said first cooling rate being in excess of said secondcooling rate, said first cooling rate being in excess of 25 F per hour,said second cooling rate being less than 125 F per hour; and hot workingsaid alloy at a temperature lower than that at which said primarycarbides dissolve, said hot working occurring within a temperature rangeof from 1,750 to 2,185 F.

2. A method according to claim 1 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.2 percent carbon, up to 2.0percent manganese, up to 2.0 percent silicon, from 5.0 to 25.0 percentchromium, up to 23 percent cobalt, up to percent molybdenum, up to 10.0percent titanium, up to 5 percent aluminum, up to 0.05 percent boron, upto 0.5 percent zirconium, up to 40 percent iron, up to 8.0 percent ofmetal from the group consisting of columbium, tantalum and hafnium, upto 2.0 percent vanadium, up to 10 percent tungsten, up to 0.5 percentrhenium, up to 0.02 percent of metal from Group II A of the periodictable, up to 0.5 percent of rare earth metal, balance essentiallynickel, said percentage of nickel being at least 40 percent.

3. A method according to claim 1 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.15 percent carbon, up to 1.0percent manganese, up to 1.0 percent silicon, from -23 percent chr0-mium, from 10 to 18' percent cobalt, from 3 to 6 percent molybdenum,from 2 to 3.5 percent titanium, from 1.0 to 2.0 percent aluminum, from0.0025 to 0.0125 percent boron, from 0.02 to 0.2 percent zirconium, upto 2 percent iron, up to 4.0 percent of metal from the group consistingof columbium, tantalum and hafnium, up to 0.5 percent vanadium, up to0.02 percent of metal from Group II A of the periodic table, up to 0.5percent of rare earth metal, balance essentially nickel.

4. A'method according to claim 1 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.15 percent carbon, up to 2.0percent manganese, up to 1.0 percent silicon, from 5.0 to 15.0 percentchromium, up to 10.0 percent cobalt, from 2 to 7 percent molybdenum,from 1.0 to 3.75 percent titanium, up to 2 percent aluminum, up to 0.05percent boron, from 25 to 40 percent iron, balance essentially nickel.

5. A method according to claim 1 wherein said nickel base alloy is agamma prime strengthened alloy.

6. A method according to claim 1 wherein said first cooling rate is inexcess of 70 F per hour and said second cooling rate is less than 60 Fper hour.

7. A method according to claim 6 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.2 percent carbon, up to 2.0percentmanganese, up

to 2.0 percent silicon, from 5.0 to 25.0 percent chromium, up to 23percent cobalt, up to 10 percent molybdenum, up to 10.0 percenttitanium, up to 5 percent aluminum, up to 0.05 percent boron, up to 0.5percent zirconium, up to 40.0 percent iron, up to 8.0 percent of metalfrom the group consisting of columbium, tantalum and hafnium, up to 2.0percent vanadium, up to 10 percent tungsten, up to 0.5 percent rhenium,up to 0.02 percent of metal from Group II A of the periodic table, up to0.5 percent of rare earth metal, balance es- 'sentially nickel, saidpercentage of nickel being at least 40 percent.

8. A method according to claim 6, wherein said nickel base alloyconsists essentially of, in weight percent, up to 0.15 percent carbon,up to 1.0 percent manganese, up to 1.0 percent silicon, from 15-23percent chromium, from 10 to 18 percent cobalt, from 3 to 6 percentmolybdenum, from 2 to 3.5 percent titanium, from 1.0 to 2.0 percentaluminum, from 0.0025 to 0.0125 percent boron, from 0.02 to 0.2 percentzirconium, up to 2 percent iron, up to 4.0 percent of metal from thegroup consisting of columbium, tantalum and hafnium, up to 0.5 percentvanadium, up to 0.02 percent of metal from Group 11 A of the periodictable, up to 0.5 percent of rare earth metal, balance essentiallynickel.

9. A method according to claim 6 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.15 percent carbon, up to 2.0percent manganese,

.up to 1.0 percent silicon, from 5.0 to 15.0 percent chromium, up to10.0 percent cobalt, from 2 to 7 percent molybdenum, from 1.0 to 3.75percent titanium, up to 2 percent aluminum, up to 0.05 percent boron,from 25 to 40 percent iron, balance essentially nickel.

10. A method according to claim 6 wherein said nickel base alloy is agamma prime strengthened alloy.

11. A method according to claim 1 wherein said hot working occurs withina temperature range of from l,800 to 2,150 F.

12. A method according to claim 1 wherein said ingot is homogenized fora period of time in excess of 4 hours.

13. A method according to claim I wherein said ingot is homogenized at atemperature of at least 2,250" F.

14. A method according to claim 13 wherein said nickel base alloyconsists essentially of, in weight percent, up to 0.2 percent carbon, upto 2.0 percent manganese, up to 2.0 percent silicon, from 5.0 to 25.0percent chromium, up to 23 percent cobalt, up to 10 percent molybdenum,up to 10.0 percent titanium, up to 5 percent aluminum, up to 0.05percent boron, up to 0.5 percent zirconium, up to 40.0 percent iron, upto 8.0 percent of metal from the group consisting of columbium, tantalumand hafnium, up to 2.0 percent vanadium, up to 10 percent tungsten, upto 0.5 percent rhenium, up to 0.02 percent of metal from Group 11 A ofthe periodic table, up to 0.5 percent of rare earth metal, balanceessentially nickel, said percentage of nickel being at least 40 percent.

15. A method according to claim 13 wherein said nickel base alloyconsists essentially of, in weight percent, up to 0.15 percent carbon,up to 1.0 percent manganese, up to 1.0 percent silicon, from 15-23percent chromium, from 10 to 18 percentcobalt, from 3 to 6 percentmolybdenum, from 2 to 3.5 percent titanium, from 1.0 to 2.0 percentaluminum, from 0.0025 to ganese, up to 1.0 percent silicon, from 5.0 to15.0 percent chromium, up to 10.0 percent cobalt, from 2 to 7 percentmolybdenum, from 1.0 to 3.75 percent titanium, up to 2 percent aluminum,up to 0.05 percent boron, from 25 to 40 percent iron, balanceessentially nickel.

17. A method according to claim 13 wherein said nickel base alloy is agamma prime strengthened alloy.

* III

2. A method according to claim 1 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.2 percent carbon, up to 2.0percent manganese, up to 2.0 percent silicon, from 5.0 to 25.0 percentchromium, up to 23 percent cobalt, up to 10 percent molybdenum, up to10.0 percent titanium, up to 5 percent aluminum, up to 0.05 percentboron, up to 0.5 percent zirconium, up to 40.0 percent iron, up to 8.0percent of metal from the group consisting of columbium, tantalum andhafnium, up to 2.0 percent vanadium, up to 10 percent tungsten, up to0.5 percent rhenium, up to 0.02 percent of metal from Group II A of theperiodic table, up to 0.5 percent of rare earth metal, balanceessentially nickel, said percentage of nickel being at least 40 percent.3. A method according to claim 1 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.15 percent carbon, up to 1.0percent manganese, up to 1.0 percent silicon, from 15-23 percentchromium, from 10 to 18 percent cobalt, from 3 to 6 percent molybdenum,from 2 to 3.5 percent titanium, from 1.0 to 2.0 percent aluminum, from0.0025 to 0.0125 percent boron, from 0.02 to 0.2 percent zirconium, upto 2 percent iron, up to 4.0 percent of metal from the group consistingof columbium, tantalum and hafnium, up to 0.5 percent vanadium, up to0.02 percent of metal from Group II A of the periodic table, up to 0.5percent of rare earth metal, balance essentially nickel.
 4. A methodaccording to claim 1 wherein said nickel base alloy consists essentiallyof, in weight percent, up to 0.15 percent carbon, up to 2.0 percentmanganese, up to 1.0 percent silicon, from 5.0 to 15.0 percent chromium,up to 10.0 percent cobalt, from 2 to 7 percent molybdenum, from 1.0 to3.75 percent titanium, up to 2 percent aluminum, up to 0.05 percentboron, from 25 to 40 percent iron, balance essentially nickel.
 5. Amethod according to claim 1 wherein said nickel base alloy is a gammaprime strengthened alloy.
 6. A method according to claim 1 wherein saidfirst cooling rate is in excess of 70* F per hour and said secondcooling rate is less than 60* F per hour.
 7. A method according to claim6 wherein said nickel base alloy consists essentially of, in weightpercent, up to 0.2 percent carbon, up to 2.0 percent manganese, up to2.0 percent silicon, from 5.0 to 25.0 percent chromium, up to 23 percentcobalt, up to 10 percent molybdenum, up to 10.0 percent titanium, up to5 percent aluMinum, up to 0.05 percent boron, up to 0.5 percentzirconium, up to 40.0 percent iron, up to 8.0 percent of metal from thegroup consisting of columbium, tantalum and hafnium, up to 2.0 percentvanadium, up to 10 percent tungsten, up to 0.5 percent rhenium, up to0.02 percent of metal from Group II A of the periodic table, up to 0.5percent of rare earth metal, balance essentially nickel, said percentageof nickel being at least 40 percent.
 8. A method according to claim 6,wherein said nickel base alloy consists essentially of, in weightpercent, up to 0.15 percent carbon, up to 1.0 percent manganese, up to1.0 percent silicon, from 15-23 percent chromium, from 10 to 18 percentcobalt, from 3 to 6 percent molybdenum, from 2 to 3.5 percent titanium,from 1.0 to 2.0 percent aluminum, from 0.0025 to 0.0125 percent boron,from 0.02 to 0.2 percent zirconium, up to 2 percent iron, up to 4.0percent of metal from the group consisting of columbium, tantalum andhafnium, up to 0.5 percent vanadium, up to 0.02 percent of metal fromGroup II A of the periodic table, up to 0.5 percent of rare earth metal,balance essentially nickel.
 9. A method according to claim 6 whereinsaid nickel base alloy consists essentially of, in weight percent, up to0.15 percent carbon, up to 2.0 percent manganese, up to 1.0 percentsilicon, from 5.0 to 15.0 percent chromium, up to 10.0 percent cobalt,from 2 to 7 percent molybdenum, from 1.0 to 3.75 percent titanium, up to2 percent aluminum, up to 0.05 percent boron, from 25 to 40 percentiron, balance essentially nickel.
 10. A method according to claim 6wherein said nickel base alloy is a gamma prime strengthened alloy. 11.A method according to claim 1 wherein said hot working occurs within atemperature range of from 1,800* to 2,150* F.
 12. A method according toclaim 1 wherein said ingot is homogenized for a period of time in excessof 4 hours.
 13. A method according to claim 1 wherein said ingot ishomogenized at a temperature of at least 2,250* F.
 14. A methodaccording to claim 13 wherein said nickel base alloy consistsessentially of, in weight percent, up to 0.2 percent carbon, up to 2.0percent manganese, up to 2.0 percent silicon, from 5.0 to 25.0 percentchromium, up to 23 percent cobalt, up to 10 percent molybdenum, up to10.0 percent titanium, up to 5 percent aluminum, up to 0.05 percentboron, up to 0.5 percent zirconium, up to 40.0 percent iron, up to 8.0percent of metal from the group consisting of columbium, tantalum andhafnium, up to 2.0 percent vanadium, up to 10 percent tungsten, up to0.5 percent rhenium, up to 0.02 percent of metal from Group II A of theperiodic table, up to 0.5 percent of rare earth metal, balanceessentially nickel, said percentage of nickel being at least 40 percent.15. A method according to claim 13 wherein said nickel base alloyconsists essentially of, in weight percent, up to 0.15 percent carbon,up to 1.0 percent manganese, up to 1.0 percent silicon, from 15-23percent chromium, from 10 to 18 percent cobalt, from 3 to 6 percentmolybdenum, from 2 to 3.5 percent titanium, from 1.0 to 2.0 percentaluminum, from 0.0025 to 0.0125 percent boron, from 0.02 to 0.2 percentzirconium, up to 2 percent iron, up to 4.0 percent of metal from thegroup consisting of columbium, tantalum and hafnium, up to 0.5 percentvanadium, up to 0.02 percent of metal from Group II A of the periodictable, up to 0.5 percent of rare earth metal, balance esSentiallynickel.
 16. A method according to claim 13 wherein said nickel basealloy consists essentially of, in weight percent, up to 0.15 percentcarbon, up to 2.0 percent manganese, up to 1.0 percent silicon, from 5.0to 15.0 percent chromium, up to 10.0 percent cobalt, from 2 to 7 percentmolybdenum, from 1.0 to 3.75 percent titanium, up to 2 percent aluminum,up to 0.05 percent boron, from 25 to 40 percent iron, balanceessentially nickel.
 17. A method according to claim 13 wherein saidnickel base alloy is a gamma prime strengthened alloy.